Of all the sunny blondes of the 1970s, Suzanne Somers was the sunniest. She had the face, the figure, the hair, the smile, the giggle, the wiggle, and enough good humor to make her breakout “dumb blond” character on “Three’s Company” lovably watchable rather than cloying or offensive.

Being a bombshell can bring a certain level of success, but it takes a special kind of charisma and drive to remain famous for more than 50 years. Ms. Somers’s alchemy derived from a combination of innocent sex appeal, nostalgia (for the pop culture ’70s fun she represented) and a canny understanding of the American cult of personality.

She figured out early on how to make herself the center of a vast business enterprise, merchandising everything from her physical appearance right down to her hormone levels, her gut bacteria levels, her marriage, even her protracted battle with breast cancer. Yes, she was a saleswoman, but not in an unpleasantly aggressive way. And she seemed so happy about everything she did, with an air of disarming innocence that deflected any sense of manipulation or personal need.

Ms. Somers may have looked like a winking promise of erotic pleasure, a sexy open secret, but “Three’s Company” never let her character, Chrissy Snow, in on her own secret. Part buxom cheerleader — in tiny shorts and tight tank tops — and part oversize baby doll, with a goofy laugh and odd, slightly askew pigtails, she invited ogling but never ogled back, absolving viewers of any prurience.

But offscreen, Ms. Somers knew her worth, and when she asked for a salary equal to her co-star John Ritter’s, she was fired. Although she returned to series television in the 1990s sitcom “Step by Step,” she never quite recaptured the TV lightning of “Three’s Company.”

Instead, she built a new, different kind of fame, becoming an entrepreneur of the booming wellness and beauty industries. She courted ridicule but made a fortune hawking gadgets like the Thighmaster, a resistance device operated by opening and closing the knees.

There was something racy about this large, snakelike object held between the legs — even its name was suggestive — but it was all for the wholesome purpose of fitness. Ms. Somers had staked out her territory. She was sex without menace, the sparkly girl — then lady — next door who was happy to invite you in and show you how to be just like her: fit, healthy, young and beautiful (within certain conventional parameters including: thin, white and heterosexual).

Her four-decade empire expanded to include exercise videos (the Somersize method); how-to books (on fitness, marriage, cooking and dieting); makeup and hair care; fashion; even a line of olive oils. She made infomercials, personal appearances and worked the talk show circuit. She also shared the darker sides of her life: Her memoir, “Keeping Secrets,” revealed her past as the daughter of an alcoholic.

When she was diagnosed with breast cancer in 2000, Ms. Somers incorporated that struggle too into her public persona and business ventures. After surgery and radiation, she eschewed chemotherapy for her cancer, vowing to find more natural means to maintain her health, including following an organic diet and reducing chemical exposure.

Eventually, Ms. Somers created and sold merchandise based on these pursuits: organic cosmetics, dietary supplements, “gut renewing superfoods,” in addition to writing several books about alternative treatments for cancer and other diseases, including “Knockout: Interviews With Doctors Who Are Curing Cancer” and “Tox-Sick: From Toxic to Not-Sick.” These books drew grave rebukes from doctors who accused her of spreading misinformation

Through it all, Ms. Somers stayed true to her 1970s image: long, straight blond hair with the brow-grazing bangs, permanent golden tan and bronze makeup, off-the-shoulder blouses. Somehow, though, this never looked odd or inappropriate. While she did not discuss plastic surgery, she did credit yet another gadget for her good looks: the “facemaster,” a microcurrent device that purported to rejuvenate sagging facial muscles. (In her infomercial for this $250 item, Ms. Somers referred to it as “a face-lift machine” and “my No. 1 beauty secret.”)

The personal morphed seamlessly into the commercial, as Ms. Somers wrote several books about maintaining a vital marriage and about bolstering her libido (and her husband’s!) with so-called bioidentical hormones, which she touted as “the key to her happiness” and “the fountain of youth.” (This too brought pushback from the medical community, which accused Ms. Somers of promoting dangerous, unscientific cures.)

In recent years, Ms. Somers became a frequent presence on social media. She turned out dozens of Facebook Live videos filmed in her sunny, lavishly appointed home in Palm Springs, Calif., in which she chatted with her husband and other friends or family members, while cooking, applying makeup or modeling clothes, always while using — and hence, selling — her own products.

These were textbooks examples of lifestyle branding at work: A relatable famous person invites viewers into her enviable home and then offers to sell them the objects necessary to reproduce some version of that life in their own, humbler homes. In the end, Suzanne Somers’s own quest and career mirrored almost perfectly some of America’s favorite fantasies. Just consider some of her book titles: “Fast and Easy,” “Ageless,” “Get Skinny,” “Sexy Forever.” Together, they read like a telegram sent straight from America’s id.